To add to the last answer yes indeed you need the air gap, using a feeler gauge go around and make sure you have the same distance all around if not make sure there is no wear on the brake pad you can take the brake by inserting the brake release bolts. Measure pad with caliper if there's no wear on it, then you might need to add spacers or shims to have an equal air gap all around.

email me if you need pictures ic3balandran at yhoo dot com

you get the book to be sure of the specs, and adjust the "air gap" with a feeler gage, and if the rotor has ANY wear, replace all the pad plates and the rotor.